450 USD for Visual Age C++
3.0?
That quite a fantasy price.

should be more like this.... Not version 3.0 but version
4.0 for AIX and x86 for 200 USD.
https://www.ebay.de/itm/167930366486But all this is wayy to expensive. I got my copy for
40 USD five years ago. Considering nobody would ever make money with this anymore. So why would it be an expensive software still? This is nothing more but a relic of the past. If you'd like to actually develop for OS/2 or Windows NT, you could use OpenWatcom, which is free of charge.
Anyway.. I'd advise to wait until this software is available again for a decent price. This is not for production anymore, but rather a museum pice.
Mathias